The use of annular seals to form a gas tight barrier between two concentric members is well known. Likewise, the use of such seals to provide a gas tight barrier about rotatable concentric members is also known. For more complex arrangements having multiple concentric rotatable members having axially extended appendages and subject to harsh local environments, certain adaptations may be required to provide an annular seal which is both effective and practicable for achieving the desired sealing effect without impeding the movement of the rotatable members.
One such application, for example, is the exhaust nozzle of a gas turbine engine having a plurality of thrust vectoring flaps and surfaces for interacting with the high temperature engine exhaust gases. One particular configuration requiring an annular seal is a two dimensional thrust vectoring nozzle having a pair of spaced apart vertical sidewalls defining the lateral boundaries of the exhaust nozzle flow path and upper and lower movable flap assemblies for defining variable upper and lower gas path boundaries whereby nozzle outlet throat area and thrust direction may be changed by manipulation of such upper and lower flap assemblies.
In particular, one 2-D nozzle arrangement includes a convergent flap extending transversely between first and second spaced apart sidewalls and secured at each span end thereof to a rotatable first member having a flat and annular surface disposed within the corresponding sidewall. This particular nozzle arrangement also includes a semi-cylindrical arc valve, rotatable about a common axis with the convergent flap and comprised of a arcuate member extending between first and second annular rims disposed concentrically about the first members.
Rotation of the arc valve at the proper time admits a flow of exhaust gas into an alternate gas exhaust flow passage for thrust reversing and/or vectoring as desired. The annular region defined by the circumference of each corresponding first member, annular rim, and surrounding sidewall must be sealed against the high temperature, elevated pressure exhaust gases flowing within the nozzle to avoid undesirable leakage of the exhaust gases into the surrounding flap structure which includes supporting bearings, linkages, and other relatively temperature sensitive structure. As exhaust gas temperatures in an afterburning mode may reach 4,000F (2,200C) or higher and have a pressure of 30-50 psig (200-350 kPa), the annular seal for this region must not only accommodate the independent movement of the convergent flap and first member and the surrounding annular rim and arc valve, but also must achieve an effective and temperature resistant gas tight seal against the high temperature, high pressure exhaust gases contained within the exhaust nozzle.